In recent years, with advance in digital technology, electronic devices such as mobile information devices and information home appliances have been developed to provide higher functionality. As the electronic devices provide higher functionality, miniaturization and an increase in speed of semiconductor devices for use with the electronic devices are making rapid progress. Among them, the use of large capacity nonvolatile memory, represented by flash memory, is rapidly expanding. Furthermore, as a next-generation new nonvolatile memory replacing the flash memory, there is on-going research and development of nonvolatile memory devices using what is called a variable resistance element (for example, see PTL 1).
Here, the variable resistance element refers to an element which has a characteristic in which a resistance value reversibly changes depending on electric signals, and further can store therein information corresponding to the resistance value in a nonvolatile fashion. Specifically, the variable resistance element includes a variable resistance layer between a first electrode layer and a second electrode layer. In the case of a bipolar variable resistance element, when voltage pulses having different polarities are applied to the first electrode layer and the second electrode layer of the variable resistance element, resistance change phenomenon occurs in the variable resistance layer. Specifically, when a negative voltage pulse is applied between the electrodes, the resistance state of the variable resistance layer turns to a low resistance state. In contrast, when a positive voltage pulse is applied between the electrodes, the resistance state of the variable resistance layer changes from the low resistance state to a high resistance state. A nonvolatile memory device using the variable resistance element is a memory which writes and reads records, utilizing at least binary values (two states) which are the high resistance state and the low resistance state of the variable resistance layer.
PTL 1 relates to the variable resistance layer of the nonvolatile memory device, and discloses a variable resistance element using, as the variable resistance layer, a stack of tantalum oxide layers having different oxygen content percentages.